Multi-color storage tube



Dec. 31, 1957 s. T. sMlTH ETAL MULTI-COLOR STORAGE TUBE 2 Sheets-Sheet l Filed Oct. .2. 1956 Sig ..2 225@ wworo coro 02mm.

SIDNEY Tf SMITH,

LORIN. L. VANT- HULL,

ATTORNEY De@ 31,1957 s. T. SMITH ETAL 2,818,524

- MULTI-COLOR STORAGE TUBE SORGE SURFACE POTENTIAL RELATIVE TO POTENTIAL OF FLOOD SUA CATHODE l: Hg. 2. l `s|DNEY T. SMITH,

l LoFuNA l..l vANT- HULL,

INVENToRs Murri-coton sronaon TUBE Sidney T. Smith, Washington, D. C., and Lor-in L. Vant- Hull, Los Angeles, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Dela- Ware Application October 2, 1956, Serial No. 613,413

Claims. (Cl. 315-12) This invention lrelates to a direct-viewing half-tone type color storage tube and more particularly to a directviewing storage tube for presenting a radar display wherein signals are presented in various degrees of brightness and color. That is, in the tube of the present invention, multiple colors are employed to produce a presentation having an increased range of half-tones and not to reproduce a scene in color.

It is an object of this invention to produce a half-tone type storage tube wherein variations in tone appear in different colors.

Another object of the invention is to provide a directviewing type storage tube particularly adapted for producing a radar presentation wherein target echo signals normally appear in a different color from that of noise signals.

Stili another object of the invention is to provide an improved multi-color half-tone storage tube which requires no special convergence or color purity circuits or special electron beam deection components and, in addition, has a brightness and writing speed several times that of conventional color storage tubes which employ a shadow mash.

According to the invention, a conventional phosphor dot viewing screen is employed which, in the event three colors are used, has each phosphor dot of a particular color touching phosphor dots of different colors. A storage screen with its associated collector grid is disposed adjacent to and coextensive with this phosphor dot viewing screen. This storage screen is characterized by the fact that it has one aperture disposed in alignment with each phosphor dot of the Viewing screen. Further, the size of each aperture in alignment with a particular color of dot is dierent from the apertures in alignment with the remaining colors. Thus, if the viewing screen is, for

example, composed of red, blue and green phosphor dots,

the area of apertures in alignment with the red dots may, for example, be six times the area of the apertures in alignment with the blue dots, which apertures may, in turn, be six times as large as the apertures in alignment with the green dots. Also provided is an electron writing gun for producing a charge pattern on the storage surface of the storage screen and a flood gun for directing iiood electrons uniformly over the entire area of the storage scre-n.

ln operation the cathode of the oo-d gun is operated at a potential positive with respect to the potentials constituting the charge pattern produced on the storage surface by the electron writing gun. ln producing the charge pattern, the extent to which an elemental area of storage surface is charged positive is determined by the amplitude of the signal applied to the intensity grid of the electron writing gun. As in present day direct-viewing half-tone storage tubes, the charge on the storage surface controls the flow of flood electrons through the storage screen to the viewing screen. In the tube of the present invention, however, due to the different sizes of the apertures in alignment with the different colored phosphor dots, a low level signal will produce a charge on the storage surface which will allow ood electrons to ilow only through the larger apertures in alignment with the red dots. As the signal becomes increasingly greater, a percent brightness will be reached on the red dots and flood electrons will commence to llow through the smaller apertures in alignment with the blue dots. As the amplitude of the signal mcreases still further, a charge is produced on the storage surface which will allow 1G() percent brightness on both the red and blue dots and will commence to allow ood electrons to flow through the apertures in alignment with the green dots. Finally, a charge of sufficient magnitude is produced on the storage surface to allow sumcient food electrons to ow through the apertures in alignment with the red, blue and green apertures to co1'- respond to 100 percent brightness. The presentation on the viewing screen corresponding to this charge will appear white. As is evident from the above, no color mask is required to produce the different colors in the device of the present invention in contrast with most present day color storage tubes. This, of course, greatly enhances eiciency of operation and the writing speed capable of being achieved.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, f

wherein:

Fig. 1 shows a cross-sectional schematic view of one embodiment of the present invention;

Fig. 2. shows an enlarged portion of the phosphor dot viewing screen and a cut-away portion of the storage screen; and

Fig. 3 shows the relative degrees of brightness on the red, blue and green apertures for various potentials on the storage surface.

Referring now to the drawings, Fig. 1 shows a directviewing storage tube in accordance with the present invention. This tube comprises an evacuated envelope 1t) which includes a `comparatively large cylindrical section 11 which has a non-axially aligned neck portion 12 at the left extremity, as viewed in the drawing, for housing an electron gun 14 for producing an electron beam of elemental cross-sectional area and horizontal and vertical deflecting plates 1S and 16, respectively, for controlling the deflection of the electron beam. The right extremity of the cylindrical portion 11 of evacuated envelope 10, as viewed in the drawing, has an extension which constitutes an annular metallic ring 1S. This annular metallic ring 1S is, in turn, sealed off by a face plate Ztl.

A viewing screen 22 is disposed on the inner surface of the face plate 20. This viewing screen 22 includes a transparent conductive coating 23, such as Nesa, disposed over the entire inner surface of face plate 20 and in electrical Contact with the metallic annular ring 13 of evacuated envelope 10. An array of phosphor color dots are then disposed on the transparent conductive coating 23 in alignment with'the storage mesh apertures. These dots may, for example, be disposed on `the transparent conductive coating 22 in a conventional manner-by using a shadow mask which matches the storage mesh to 'be used as -a master. In the described embodiment, the. colors of the phosphor dots .are chosen so that approximately white light is produced when all three colors are at full brilliance. Colors of phosphor dots capable of producing white light are red, blue and green. to Fig. 2, there is shown an enlarged portion of the viewing screen 22. In this gure the dots 2S are red, dots 26 are blue and dots 27 are of green phosphor. Each dot is ofthe order of 13 mils in diameter and is in contact only with dots of another color. In operation the screen 22 is maintained at a potential `of the order of Patented nec. 31,1957

Referring 5,000"volts positive with respect to ground by means of a connectionfrom the annular ring 18"to the positive terminal Iof a battery 30, thefnegative terminal of which is connected to ground.

Disposed adjacent to andjco-extensivewith:viewing..

screen 22 are a storage screen,32'and.its :associated co1- lector grid 34 supported by concentric meta1lic,rings.33 and 35, respectively.' The .storage screen 32 comprisesa thin-sheet of metalV 36 composed,y for Aexamplepof. cu. pronickel. The metallic sheet 36 is. of .the `orderof from 3 to 6 mils thick. As shown in Fig. 2,4 the cupronickel Sheet 36 is provided withapertures inalignmentwith each.

phosphor `dot on the viewin'gscreen 22... Aspreviouslyy specified, the diameter of .theapertures in ,alignmentwith the different colors of phosphor do'ts are different. Inparf ticular, the diameterof apertures 37"in alignmentwith theredphosphor dots isi approximately,6.25.,mils the- 1 diameter of apertures 38"in alignment with the blue phos-.. phor dots '36" is `approxima=telyr25 mils,' and thediametet. of 'theapertures 39in' alignment with the greentphos-a. phor dotsy 27 is approximately 1.0 fmil.' The storagersur face is provided by a layer 40' of *dielectric material dis-A posed over the remaining areas .of .metallic sheet 36 on. the side-thereof `opposite the viewing screenr22'. Thislayer 40 `of^dielectric material may constitute, for example, a layer of magnesium fluoride of the order of 'microns thickevaporated on one side' ofthe cupronickel sheet 36.

Disposed adjacentv to and co-exte'nsive with vthe storage.

surface sideof 'storage screen 32" is fthe. collector .grid 't 34: The` collector grid may be provided v'by either aw woven .or electroformed mesh ,havinga pitch of.approxi.

enablingit to beerased vv'by-the flood-electrons-'as will be lhereinafter explained inl more detail.

As previously .speciedf-neck portion'-12 of evacuated" envelopel houses electron-#writing gun14'together-with1 the-horizontalr and vertical deecting plates 15 4and "16,'

respectively. Thel gun may, iof/course, lbef-i'nagneticallyrdeflected equally-well in vcases where-- magnetic, rotatingr4 deection yokes would be used, i. e., for 'as-*Paludisplay. The-electron ywriting gun- 14 includes--a 'cathodeL 46 and an intensity grid 47'.v The cathode'46'-fof gun -14- is maintained at a potential-of -the-'orderof -3000l-volts with'l-respect togroundbymeans vof a connectionvfthere-I fronrftorthe4 negative terminal Yof battery 48-,fthe-positivez potentialfof. theorder Yof 75 volts negative vwith respect to cathode 46. Thisisiaocomplishedx bymeansof a.con-

52the positive-terminalof^which-^is referenced "tor-the'n cathode 46.h Means-for'modulatin'g'the intensity ofthe electron-writing beam is provided by a connection from an input terminal 53' through a capacitor 54 'acrossfthe load resistor 'to the intensity grid `47fof gun,14.

The electron beam produced by, electron writin'ggun.. 14 isi scanned over; the storage screenzinth'e, desired manner by means of horizontal and.;vertical-'deflection voltages generated `byhorizontal .andwertical -deflectiongt voltage ,generators 56 and.58, .respeotively,l Theffltioriff.`

zontal deflection signal is applied .to i .the @horizontal f .dem f eeting. plate .15 through, .capacitors 59,. 60;acrossisolating-gs resistors 61, 62. Similarly, the vertical deflection signal is applied to the vertical deflecting plates 16 through' capacitors 63, 64 across isolating resistors 65, 66. The horizontal and Vertical deflecting plates 15, 16 are main.I tained at la quiescent potential of the order of 100 volts positive with respect to groundby means of connections from the common junctions between resistors 61, 62 and 65, 66 to a tap 68' of. a potentiometer 70 which, in turn,

is connected Aacross theterminals ofthe battery 42. In..

addition. to lthe above, an equipotential region is maintained intermediate the deecting plates 15,16 and/the annular ring 18 by means of a conductive coating 72 dis.- posed over the inner surface of the evacuated envelope 10 throughout this region. This conductive coating 72 may, for example, be composed ,of. Aquadag and is maintained at a potential equal to that of the quiescent potential applied to deflecting plates 1S, 16 by means of a .connection therefrom tothe tap. 68 of potentiometer 70.

A point source of flood electrons is provided by a ood gun 74 disposed along the longitudinal axis of the cylindrical. portion 11 of levacuated envelope 10 at the left extremity thereof, as viewed in the drawing. Flood gun 74 .includes acathode 76, anl intensity grid 77 which encloses the cathode 76 except for an aperture 78 disposed over4 the central portion of the cathode 76, and an annular. electrode79 vdisposed adjacent to and concentrically about the aperture 78. In operation cathode 76 of flood gun 74 is maintained at ground potential by means of a connection therefrom to ground. Further, the intensityelectrode 77 and the .annular electrode 79 are maintained atpotentials ofthe korder of -20 and +80 volts with respect to ground by means of connections therefrom to adjustable .taps 80'and 81, respectively, of a potentiometer82. The potentiometer 82 is, in turn, connected across the positive and negative terminals of a battery 84 and an intermediate terminalthereofreferenced to ground.

j According to the present invention, the operation of the. disclosed direct-viewing half-tone storage tube is similar to that of the half-tone storage tube disclosed in Patentrv No. .2,790,929 entitled Direct-Viewing Half-Tone Storage Device,.issued to Elvin E. Herman et al., on April 30, 1957 whichv patent is assigned to the same assignee as the presentapplication. In general the flood gun 74 s operated to provide a uniform collimated flow of low velocity electrons overY theentire storage area of storage screen32.. This is. accomplished by suitable adjustments on the taps 80,.-81. of potentiometer 82 which determine the potentialsapplied .to the intensity electrode 77 and annular electrode 79,.,respectively, of the ood gun- 74.

These potentials will, of course, vary somewhat with con figuration of the. tubeenvelope 10 and the potentials at which conductive coating 72 and collector grid 34 are maintained. The storage surface of storage screen 32 is prepared for writing by applying a l0 to 20 volt positive pulse generated by the pulse generator 44 to the cupronickel sheet 36 ofthe storage screen 32. Initially the flood electrons will have charged the storage surface. to the potential of the flood gun cathode 76, which potential is ground. Because of the capacitance between the storage surface and the cupronickel sheet 36, the application of the pulse to the cupronickel sheet 36 raises the potential of the storage surface by a corresponding` amount. The ood electrons then charge the storage surface to ground potential. Upon completion of the pulse, the potentials of the storage surface follow the negative excursion of the trailing edge of the pulse whereby the storage surface assumes a potential of from l0 to 20 volts negative with respect to ground.

Writing is accomplished by applying a signal to input 53, thereby .to current modulate the highfenergy-high.- current density electron beam produced by ythe-electron writing gun14. This high-energy current,-modul-atedelec.-

tron beamV is caused to scan the storage surface,y of they storage screen 32 by. the applicationyofsuitable .deflection voltages generated by horizontal and vertical voltage generators 56, 58 to the deecting plates 15, 16, respectively. As the storage screen 32 is scanned by the high energy electron beam, the storage surface is charged towards the potential of flood cathode 76 by an amount which is a function of the input signal impressed on terminal 53. The potential on the area of storage surface surrounding a given -aperture controls the dow of flood electrons through that aperture and thus controls the brightness of illumination of the corresponding phosphor dot. Because of the different sizes of the apertures aligned with each of the sets 25, 26, 27 of phosphor dots, the useful range of storage surface potential is different for each color. For example, a weak signal will allow ood electrons to flow only through the apertures 37 aligned with the red dots 25, a medium signal would allow ood electrons to flow through both the red and blue sets of apertures 37, 38 aligned-with the red and blue sets of phosphor dots 25, 26, respectively, and a strong signal would allow flood electrons to ow through all three sets of apertures 37, 38, 39 to the phosphor dots 25, 26 and 27. Thus, the resulting color produced on the viewing screen 22 depends upon the strength of the input signal initially applied on terminal 53. Because of the nature of the storage mechanism, scan-to-scan integration can also be used. For example, a weak signal which repeats on successive scans may appear red on the first scan, red-blue on the second scan and white on the third scan. This is a useful mechanism because it enables low-level signals to be easily distinguished from noise. It is to be noted that no processing of input dat-a is required, but that if it is desired to present additional information, it can easily be added to the incoming signal. For example, a white bar could be written beside selected targets.

The greater range of half-tones provided by the tube of the present invention is evidenced from a consideration of the brightness of the individual sets of phosphor dots 25, 26, 27. It is assumed that there is a logarithmic variation of sensation with brightness and that the human eye can conveniently distinguish between two levels of brightness wherein one of the primary colors differs in brightness in the two levels by a factor of three. With these considerations, diierent storage surface potentials would provide the following visual responses:

Brightness in percent Storage surface potential Level relative to flood cathode 76 Red Blue Green More negative than:

OOOOOOO OOOOOOOOOOCOO n-u-l In order to illustrate the above data, Fig. 3 shows graphs 90, 92 and 94 of the brightness level of the red, blue and green sets 25, 26 and 27 of the phosphor dots for storage surface potentials commencing from more negative than -20 volts relative to flood gun cathode 76 and increasing to a potential equal to that of ood cathode 76. It is evident that under the above assumptions there are about 21 distinguishable levels of brightness and hue between black and white, a factor of three increases over that of conventional half-tone storage tubes. It is, of course, realized that the use of a dilerent number of colors or alternate combinations thereof is obviously within the scope of the teachings of this specication. Itis further evident that the tube of the present invention may incorporate an aluminized viewing screen 22; a magnetically deflected writing gun 14; a ring-type ood gun 74; continuous erasure elfected by the application of a train of +10 to +20 volt pulses of short duration to the storage screen 32 by the pulse generator 44, and of such an amplitude and duration as to erase noise, but allow signal integration from scan-to-scan; and use `of color dots corresponding in size to the beam of flood electrons passing through each size aperture at zero storage surface potential, e. g., 5, 10, 15 mils, respectively.

What is claimed is:

l. A direct-viewing multi-color half-tone storage tube comprising a viewing screen having a plurality of integrated sets of different colored fluorescent dots; a storage screen disposed adjacent to and co-extensive with said viewing screen, said storage screen having a single aperture in alignment with each of said fluorescent dots of said viewing screen, the size of the apertures in alignment with any one of said sets Vof dots being equal and the sizes of apertures in alignment with different colored liuorescent dots being different; means for producing a charge pattern on said storage screen; and means for directing flood electrons uniformly over said storage screen whereby the charged storage area surrounding each aperture controls the iiow of said flood electrons therethrough to said viewing screen to produce a presentation wherein diierent potential levels of said charge pattern correspond to different colors.

2. The direct-viewing multi-color half-tone storage tube as dened in claim 1 wherein said lood electrons emanate from a source maintained at a predetermined potential level that is positive with respect to the potentials constituting said charge pattern.

3. The 'direct-viewing multi-color half-tone storage tube as defined in claim 2 including means for increasing the potentials constituting said charge pattern to potential levels that are positive with respect to the potential of said source of ood electrons, thereby to erase said charge pattern.

4. The direct-viewing multi-color half-tone storage tube as defined in claim 1 wherein said viewing screen has three sets of different colored fluorescent dots, said dots being arranged so that the periphery of the dots in any one set is contiguous to the periphery of the dots in the remaining two sets.

5. The direct-viewing multi-color half-tone storage tube as defined in claim 4 wherein said three sets of fluorescent dots produce the colors red, blue and green upon bombardment by electrons, the apertures in said storage screen in alignment with the red dots being substantially six times greater in area than the apertures in alignment with said blue dots, which apertures are, in turn, six times greater in area than the apertures in alignment with said green dots.

References Cited in the iile of this patent UNITED STATES PATENTS 2,186,393 Ring Ian. 9, 1940 2,532,339 Schlesinger Dec. 5, 1950 2,728,872 Smith Dec. 27, 1955 2,755,402 Morrell July 17, 1956 2,761,089 Haeft Aug. 28, 1956 2,788,466 Hansen Apr. 9, 1957 2,790,929 Herman Apr. 30, 1957 

